Recycling of catalyst coated membrane components

Abstract

A method of recycling a waste ionomer material comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising: (a) mixing the waste ionomer material to homogeniz

Description

Field This specification relates to recycling methods for components of catalyst coated membranes such as those used in fuel cells and hydrogen producing water electrolysers. Background Fuel cell and hydrogen producing water electrolyser production is set for rapid growth as investment is placed into the global hydrogen economy. Catalyst coated membranes (CCMs) are a major functional component of both fuel cells and electrolysers. Such CCMs generally comprise a conductive polymer membrane coated on either side by a catalyst containing layer. The CCMs are configured to drive oxidation and reduction reactions and support proton and electron transport, these processes been required for the fuel cell and electrolyser technologies to function. While variations in CCM component materials and configurations exist according to functional performance requirements in end use applications, they generally contain several components of value including one or more platinum group metal (PGM) catalysts and one or more proton conducting polymers. Typically, the membrane is formed of one or more ionomers such as perfluorosulfonic-acid (PFSA) ionomers. Ionomer may also be provided in one or both of the catalyst layers. The ionomer in the catalyst layers may be the same or different to the ionomer in the main membrane component and / or in the other catalyst layer(s). A CCM may comprise two different catalysts, one for driving an oxidation reaction on one side of the CCM and one for driving a reduction reaction on the other side of the CCM. A CCM may also comprise a recombination catalyst which is provided to catalyse the recombination of hydrogen and oxygen to form water, reducing the quantity of hydrogen crossing the membrane and mixing with oxygen to form a potentially explosive mixture. A CCM may also include a metal oxide (e.g., CeCh) as a peroxide scavenger. CCM catalysts can be based on platinum group metals such as platinum, ruthenium, iridium, palladium, or mixtures thereof. The platinum group metals may be provided in elemental (metallic) form, in compound form (e.g., an oxide, such as an iridium oxide catalyst), or as a PGM-base metal alloy (e.g., PtCo). Furthermore, the PGM catalyst materials may be supported on a substrate material (e.g., carbon, such as a platinum-on-carbon catalyst comprising particles of carbon on which platinum is disposed or PtCo-on-carbon). Catalyst coated membranes (CCMs) can also be provided in combination with additional functional layers to form multi-layer membrane electrode assemblies (MEAs). Such MEAs may have 3, 5, or 7 layers for example. With the increase in CCM manufacture for fuel cells and electrolysers, there is an associated increase in CCM waste materials, including a significant volume of scrap material created during CCM manufacture (e.g., due to failure at quality control) and also an increase in end-of-life (EoL) CCMs. Since CCMs contain several components which are rare and / or valuable, including platinum group metals (notably Pt, Pd, Ir and Ru) and ionomer (both in the membrane and catalyst layers), there is a growing demand for methods of recycling such components from waste CCM materials. One current method to recover PGMs from production scrap and end-of-life CCM material involves incineration. The incineration process yields a PGM rich (typically Pt and Ir) ash which is processed via conventional PGM refining routes. However, the incineration process releases harmful and toxic gases such as CO2 and HF from the polymers that are part of the membrane. Both these gases have negative impacts as they pollute the atmosphere, increase the greenhouse effect, and / or have harmful effects in the human body. As such, there is a need for a cleaner process which reduces or eliminates the emission of these gases. In addition to the above, the incineration method destroys the ionomer component which also has significant value. As such, it would also be desirable to provide a process which is capable of recovering both PGM and ionomer components as well as providing a process which is cleaner, safer, and more environmentally friendly. Processes for recovering perfluorosulphonic acid ionomer are known. See, for example, WO2016 / 156815 and US7255798. Furthermore, processes for recovering individual PGM catalyst components are known. See, for example, US7709135. However, to enable fuel cells and electrolysers to become more sustainable technologies, there is a need for commercially viable and environmentally friendly routes to recover, separate, and recycle both the PGMs and the ionomer components from waste CCM materials including production scrap and end-of-life material. It is an aim of the present specification to address this problem. Summary of Invention As described in the background section, prior art methods have involved waste catalyst coated membrane materials being incinerated to produce a PGM rich ash which is provided to a PGM refiner for recovery of the PGMs. The PGM rich ash produced by the incineration process has the benefit of being homogenized with the PGM concentrated in the ash-like residue. The material is readily sampled and assayed by the PGM refiner to determine a representative PGM content prior to processing the material through a PGM refining process. The present applicant has developed a recycling process for waste catalyst coated membrane materials which separates and recovers both PGM materials and ionomer materials, as well as being capable of separating and recovering additional components such as base metals, carbon, and polymer reinforcement materials. This is beneficial over the aforementioned incineration process from an economic perspective in that additional valuable components are recovered. Furthermore, this is beneficial from an environmental perspective as incineration leads to generation of significant levels of CO2 and HF and is also very energy intensive. Yet another problem with the incineration route is that if the waste catalyst coated membrane materials is incinerated by a third-party company, the PGM refiner may then be unable to account for any potential metal losses between initial receipt of the material for refining and return of the ash from the third-party company. This could represent a significant metal accounting risk and route for metal loss for the PGM refiner. While providing a PGM recycling process which is also capable of recovering the ionomer addresses the aforementioned problems with the incineration route, the present inventors have identified an issue with practically implementing such a process. Since the PGM containing input material for the PGM refining process is waste ionomer material containing PGM, the PGM content is not homogenized and concentrated as in the PGM rich ash. As such, to avoid a significant metal accounting risk, the waste ionomer material should be processed to homogenize the waste ionomer material prior to sampling and assaying for PGM content. In addition, the present inventors have realized that ionomer materials come in many types and forms and can have different molecular weights, different equivalent weight, and / or different sulfonated side chains. Furthermore, waste ionomer materials may include two of more different ionomers and these different ionomers may not be uniformly distributed through the waste ionomer material. As such, to avoid a significant ionomer accounting risk, the waste ionomer material should additionally be properly assayed for ionomer content, in addition to PGM content, but only after suitable processing to homogenize the waste ionomer material to enable collection of a representative sample for both PGM content and ionomer content. In light of the above, according to one aspect of the present specification there is provided a method of recycling a waste ionomer material comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising: (a) mixing the waste ionomer material to homogenize the waste ionomer material, optionally including reducing particle size of the waste ionomer material; (b) taking a sample (or more than one sample) of the homogenized waste ionomer material, optionally including processing the sample(s) to further reduce particle size; (c) assaying the sample(s) of homogenized waste ionomer material to characterize ionomer content and platinum group metal content of the waste ionomer material; and (d) recycling the waste ionomer material to separate and recover both the ionomer and the platinum group metal materials on the basis of the ionomer content and the platinum group metal content determined by the assaying. For example, the waste ionomer material can be in the form of a membrane material which is shredded and mixed in step (a) to reduce particle size and homogenize. Furthermore, after sampling, the sample(s) of material may be further reduced in size via a milling technique prior to assaying the sample(s) of material for PGM and ionomer content. This processing is intended to ensure that assay measurements are representative for both PGM content and ionomer content of the bulk waste ionomer material. The assaying in step (c) can also include characterizing the sample for one or more other materials including one or more of base metal content, carbon content, and polymer reinforcement content in addition to ionomer content and platinum group metal content. Homogenizing, sampling, and assaying in this manner for both PGM and ionomer content (and optionally other material components) is advantageous for several reasons when implementing a recycling process which recovers both PGM and ionomer materials (and optionally other material components) from waste ionomer material. Metal and ionomer accounting risks can be avoided. The process enables a suitable price to be agreed for recycling of the waste ionomer material based on at least the ionomer content and the platinum group metal content determined by the assaying, and optionally the content of the other material(s). Additionally, or alternatively, the process enables agreement on a suitable quantity of the ionomer and platinum group metal materials to be produced from the recycling process based on the ionomer content and the platinum group metal content determined by the assaying, and optionally agreeing a quantity of the other material(s) to be produced based on the assaying results for said other material(s). Good materials accounting in this manner also ensures that batches of waste ionomer material are not required to be processed separately. Once the content of individual batches has been properly evaluated and agreed, the waste ionomer material can be mixed with one or more other waste ionomer materials from other sources prior to recycling. This gives flexibility to recycle waste ionomer materials from a range of different sources at the same time which increases process efficiency. In addition to the above, the assaying results can be used to tailor the recycling process to produce ionomer products of a target specification to meet functional end use requirements. In this regard, it has been noted that different types of ionomers are currently being used to manufacture membranes for fuel cells and electrolysers. For example, ionomer membranes can differ in their molecular weight, ionomer equivalent weight, and / or comprise ionomer with differing sulfonated side chains. It has also been proposed to blend ionomers of different types in order to fabricate membranes with adjusted properties. One problem with recycling of waste ionomer materials such as manufacturing scrap and used ionomer materials is that the materials may not have the desired compositions or properties for re-use in new applications such as new fuel cells and electrolysers. Another problem is that manufacturing scrap and used ionomer materials may have a variety of different types and compositions which are required to be recycled into new materials which meet target specifications for re-use in new applications. Yet another problem is ensuring that any recycling process for waste ionomer materials should be flexible, energy efficient, and cost effective. The present inventors have realized that the aforementioned problems can be addressed by integrating an ionomer blending process into a recycling process for waste ionomer materials in order to adjust the compositions and properties of the waste ionomer materials during recycling to meet target specifications for re-use in new applications. The assaying results for the ionomer can thus be compared with a target composition for the ionomer product after recycling and, during recycling, additional ionomer material can be blended with the waste ionomer material, the additional ionomer material being of a type and quantity selected to achieve the target composition for the ionomer product. The processes used to disperse and recycle waste ionomer materials have been found to be suitable to ensure that the different ionomers are properly blended and co-mingled at a molecular level and this enables materials to be fabricated with predictable functional performance characteristics. However, this is only accurately enabled by suitable analysis of the starting waste ionomer materials. Accordingly, the aforementioned methodology is advantageous for several reasons: it enables ionomer membrane materials to be recycled into new membrane components with modified and / or optimized compositions and properties through predictive blending; it provides greater flexibility to enable recycling of ionomer membrane materials of different types and compositions to produce new membrane components which meet target specifications; it provides flexibility to blend ionomers from different membrane materials and / or to blend ionomer from scrap or used membrane materials with virgin / fresh ionomer material during recycling; it ensures that the different ionomers are properly co-mingled at a molecular level as part of the recycling process; and it can achieve the ionomer blending in an energy efficient manner by integrating the ionomer blending step into a membrane material dispersal step as part of the membrane recycling process thus reducing costs, additional equipment requirements, and improving environmental impact. Brief Description of the Drawings For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a waste CCM recycling process according to the present specification; Figure 2 shows more detail of step (d) in Figure 1 illustrating a waste CCM recycling process comprising a platinum leach followed by an iridium leach followed by ionomer dispersion; Figure 3 shows another more detailed example of step (d) in Figure 1 illustrating a waste CCM recycling process comprising the following steps in the stated order: (i) oxidative acid leach to recover platinum; (ii) reductive acid leach to recover iridium; (iii) treatment of remaining solid ionomer material with a base to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; (v) separating the ionomer dispersion from other components, e.g., carbon and / or membrane reinforcement material; and (vi) subjecting the ionomer dispersion to an ion exchange process to re-protonate the ionomer material; Figure 4 shows FTIR data for fluorinated polymer membrane material, fluorinated polymer salt material formed after treatment in water and base, and fluorinated polymer salt material formed after treatment in water and base followed by a water wash; Figure 5 shows an example of process steps (pre-ionomer dispersion) including refluxing fluorinated polymer membrane in a basic LiOH solution to form a fluorinated polymer salt without dispersing the membrane followed by washing with water; Figure 6 is a photograph showing the membrane before (left hand side) and after (right hand side) the process steps of refluxing the membrane in a basic LiOH solution and washing with water; Figure 7 shows a further step of ionomer dispersion in solvent at elevated temperature (e.g., via autoclaving the membrane) following the treatment process as shown in Figure 5; and Figure 8 shows a further step (post-dispersion) of ion exchange to convert the dispersed polymer salt back to protonated acid form. Detailed Description As described in the summary section and illustrated in Figure 1, the present specification provides a method of recycling a waste ionomer material comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising: (a) mixing the waste ionomer material to homogenize the waste ionomer material, optionally including reducing particle size of the waste ionomer material; (b) taking a sample (or more than one sample) of the homogenized waste ionomer material, optionally including processing the sample(s) to further reduce particle size; (c) assaying the sample(s) of homogenized waste ionomer material to characterize ionomer content and platinum group metal content of the waste ionomer material; and (d) recycling the waste ionomer material to separate and recover both the ionomer and the platinum group metal materials on the basis of the ionomer content and the platinum group metal content determined by the assaying. For example, the waste ionomer material can be in the form of a membrane material which is shredded and mixed in step (a) to reduce particle size and homogenize. Furthermore, after sampling, the sample(s) of material may be further reduced in size via a milling technique prior to assaying the sample(s) of material for PGM and ionomer content. This processing is intended to ensure that assay measurements are representative for both PGM content and ionomer content of the bulk waste ionomer material. Waste ionomer material may be received as either 7-layer, 5-layer, or 3-layer MEAs (catalyst coated membrane, CCM), part-CCMs, catalyst layers or as ionomer membrane (which may or may not be PGM containing). Preliminary disassembly prior to obtaining 7-layer MEAs involves mechanical dismantling of fuel cell / water electrolyser modules to stacks by removal of peripheral components (e.g. pumps, compressors, etc.). Removal of end-plates and insulation enables separation of the stack into individual cells, which can then be further disassembled by removal of bipolar plates to 7-layer MEAs. PEMWE (proton exchange membrane water electrolysers) may contain Pt-coated porous transport layers (PTL's) which can be further refined to recover the Pt coatings. 7-layer MEAs can be disassembled to 5-layer MEAs by removal of the gas diffusion layers (GDLs) either by hand, or other mechanical or chemical delamination process. For example, treatment with water and / or another solvent can cause swelling of the membrane which can induce delamination of GDLs. The 5-layer MEAs can then be further disassembled to a 3-layer MEA / catalyst coated membrane (CCM) component by removal of associated edge seal / gasket material. This may be by a manual or mechanical cutting process, such as scissors, a guillotine, stamp / press or possibly chemical dissolution. Any remnants or wastes from this process can be further recycled to recover trace PGM. Where material is received as CCM, part-CCM, catalyst layers (CL), or PGM-containing membranes (MEM), the material can be removed from any backing or supporting material prior to size reduction, homogenization, sampling, and assaying. The homogenization, sampling and assaying process can then commence using CCM / part-CCM / CL or PGM containing membrane material. These can be reduced in size using a coarse shredding process using a rotary cutting mill, but can also be processed using another shredding technology (e.g., a rotary drum, guillotine, etc). Particle size may be reduced to a low as ~2 mm square for example. During coarse shredding, material may be wetted, or processed under an oxygen-limited (for example, under N2) and / or a humidity-controlled atmosphere. A proportion of the shredded material can then be sampled. This can be through use of a splitter on the shredder outlet, by manual sampling (e.g., spear sampler), or other recognised sampling technique. This sample may then be reduced further in particle size to <1 mm using a fine cutting mill, rotary mill, cryo-milling, etc. and further split using, for example, a rotary riffler, to obtain a sample representative of the bulk with respect to PGM and ionomer content. The assaying in step (c) characterizes both ionomer and PGM content. The assaying can also include characterizing the sample for one or more other materials including one or more of base metal content, carbon content, and polymer reinforcement content in addition to ionomer content and platinum group metal content. For example, the assaying in step (c) can follow a characterisation workflow to determine one, more, or all of the following: platinum group metal type and amount, optionally using ICP spectrometry (e.g., ICP-optical emission spectrometry and / or ICP-mass spectrometry) following a metal digestion or bulk incineration process and / or XRF (e.g., used on pelletised solid samples which may be in a supporting matrix such as wax); ionomer equivalent weight(s), optionally using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and / or titration methods and / or other spectroscopic techniques such as XRF and / or EDX; ionomer type(s), optionally using NMR, FT-IR, ion-chromatography, gel permeation chromatography (GPC), and / or elemental analysis for carbon, fluorine, sulphur, and oxygen content and / or IC combustion techniques, dynamic scanning calorimetry, XRF, EDX, fire assay, laser-ICP, mass spectrometry, UV-Vis, and / or AAS; ionomer molecular weight(s), optionally using GPC, mass spectrometry and / or melt flow index; base metal type and amount, optionally using ICP-spectrometry following a metal digestion or bulk incineration process and / or XRF; carbon content, optionally using thermal gravimetric analysis and / or thermal conductivity detection following combustion, elemental analysis, and / or IC combustion techniques; polymer reinforcement material type and amount, for example by techniques of elemental and / or thermal gravimetric analysis (e.g., DSC). Homogenizing, sampling, and assaying in this manner for both PGM and ionomer content (and optionally other material components) is advantageous for several reasons when implementing a recycling process which recovers both PGM and ionomer materials (and optionally other material components) from waste ionomer material as previously described in the summary section including: • Metal and ionomer accounting risks can be avoided, and the process enables a suitable price to be agreed for recycling of the waste ionomer material based on at least the ionomer content and the platinum group metal content determined by the assaying and optionally the content of the other material(s). • The process enables agreement on a suitable quantity of the ionomer and platinum group metal materials to be produced from the recycling process based on the ionomer content and the platinum group metal content determined by the assaying, and optionally agreeing a quantity of the other material(s) to be produced based on the assaying results for said other material(s). • Good materials accounting ensures that batches of waste ionomer material are not required to be processed separately such that once the content of individual batches has been properly evaluated and agreed, the waste ionomer material can be mixed with one or more other waste ionomer materials from other sources prior to recycling. • The assaying results can be used to tailor the recycling process to produce ionomer products of a target specification to meet functional end use requirements including, for example, comparing the assaying results for the ionomer with a target composition for the ionomer and blending additional ionomer with the waste ionomer material during recycling, the additional ionomer material being of a type and quantity selected to achieve the target composition for the ionomer. In order to check that the characterization is correct, a membrane can be fabricated using the recovered ionomer and tested to confirm it meets a target specification. The recycling in step (d) of Figure 1 may include: treating the waste ionomer material with one or more acid leaches to extract the platinum group metal material; and an ionomer dispersal step to extract the ionomer material. The leaching and dispersal steps may be performed in any order. However, one preferred methodology is shown in Figure 2 which illustrates a waste CCM recycling process comprising a platinum leach followed by an iridium leach followed by ionomer dispersion. In this example, a method of recycling a waste catalyst coated membrane material comprising an ionomer membrane, at least one catalyst comprising platinum (e.g., a platinum-on-carbon catalyst), palladium and / or ruthenium and at least one catalyst comprising iridium (e.g., an iridium oxide catalyst) is provided. The method comprises: (a) treating the waste catalyst coated membrane material with a heated solution comprising an acid and an oxidant, wherein platinum, palladium, and / or ruthenium is leached from the waste catalyst coated membrane material into the solution which is separated from remaining solid components of the waste catalyst coated membrane material; (b) after step (a), leaching iridium from the waste catalyst coated membrane material using a heated solution comprising an acid and a reducing agent and separating the solution comprising the leached iridium from remaining solid components of the waste catalyst coated membrane material; and (c) after steps (a) and (b), treating the waste catalyst coated membrane material with a heated solvent to disperse the ionomer membrane and recover a dispersion of ionomer. It has been found that performing the aforementioned steps in the stated order, it is possible to separately recover the platinum, palladium, and / or ruthenium, the iridium, and the ionomer materials without significant degrading the ionomer and ensuring that substantially all (e.g., at least 97%) of the PGMs are recovered with the platinum and iridium being separated upfront in the process. The acid used in one or both of the iridium leach and the platinum leach is preferably hydrochloric acid and optionally does not contain nitric acid. Furthermore, one or both of the solution used for the leach of platinum and the solution used for the leach of iridium are preferably heated to a temperature of: at least 50°C, 60°C, or 70°C; no more than 160°C, 120°C, 100°C, or 90°C; or within a range defined by any combination of the aforementioned lower and upper limits, wherein if the solution is heated above 100°C then this is done in a pressurized vessel. Example temperatures are around 70°C for the platinum leach and around 105°C for the iridium leach. Solutions are heated to increase leaching rate of PGMs. The oxidant can comprise, for example, a chlorate salt such as sodium chlorate solution, hydrogen peroxide, or chlorine gas. According to one preferred option, the acid used in the leach of platinum, palladium and / or ruthenium is hydrochloric acid and the oxidant is chlorine gas generated from the hydrochloric acid electrolytically in-situ. The oxidant can be added to the hydrochloric acid solution or generated in-situ after heating up to the aforementioned temperature. Alternatively, the oxidant can be added in a plurality of aliquots during heating. For example, oxidant can be added in a series of aliquots during heating. The solution for leaching platinum may have an oxidant concentration of: at least 0.001, 0.005, or 0.01 mol / l; no more than 1, 0.5, or 0.10 mol / l; or within a range defined by any combination of the aforementioned lower and upper limits (e.g., a total oxidant concentration in a range 0.01 to 0.10 mol / l). One or both of the solution used for the leach of platinum and the solution used for the leach of iridium has an acid concentration of: no less than 4 M, 5 M, 5.5 M, or 6 M; no more than 15 M, 12 M, 10 M, or 7 M; or within a range defined by any combination of the aforementioned lower and upper limits. Separation of the solution containing the leached platinum may be achieved via filtration or centrifugation. The separated solution may be concentrated by boiling the solution down to a suitable platinum concentration for further processing. Alternatively, the leachate can be recirculated to leach platinum from further waste catalyst coated membrane material, recirculation being repeated as required until a suitable or target concentration of platinum is reached. For example, after separating the solution containing the leached platinum from remaining solid components of the waste catalyst coated membrane material, the solution can be concentrated to yield chloroplatinic acid comprising at least 30 wt% Pt. One advantage of the aforementioned process is that it achieves a high yield of recovery for platinum, palladium and / or ruthenium. For example, at least 97wt% of the platinum in waste catalyst coated membrane can be recovered. Another advantage of the aforementioned process is that substantially no fluorine is leached out from the fluoropolymer membrane into the leachate using these conditions. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled separately. Secondly, leaching of fluorine into the acidic leachate can lead to the formation of HF which can result in a serious environmental health and safety risk as well as damaging downstream processing equipment. As such, avoiding HF formation provides a safer and more environmentally friendly process. Yet another advantage of the aforementioned process is that for CCMs which comprise both a platinum and an iridium oxide catalyst, which is a useful combination of catalysts for the cathode and anode catalysts respectively of a hydrogen producing water electrolyser, the leach conditions are selective for platinum and do not leach iridium to any significant extent. As such, the process represents an efficient way to separate platinum from the other components of such a waste CCM while leaving remaining CCM components intact to be processed separately. The iridium (which may be in the form of an iridium oxide, mixed iridium oxide, or supported iridium oxide) can be separately extracted using an acid leaching process. This differs from that used for leaching of platinum. In particular, a reducing agent (e.g., hydrazine) rather than an oxidizing agent is used for the iridium leach. Optionally, the reducing agent is added to the waste catalyst coated membrane material first and then followed by addition of the acid. One advantage of the aforementioned process is that it achieves a high yield of recovery for iridium. For example, at least 95wt% of the iridium in waste catalyst coated membrane can be recovered. Another advantage of the aforementioned process is that substantially no fluorine is leached out from the fluoropolymer membrane into the leachate using these conditions. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled separately. Secondly, leaching of fluorine into the acidic leachate can lead to the formation of HF which can result in a serious environmental health and safety risk as well as damaging downstream processing equipment. As such, avoiding HF formation provides a safer and more environmentally friendly process. As previously indicated, the iridium leaching conditions are such that they do also leach a significant quantity of platinum (e.g., 20 - 40% of the Pt) if still present in the waste catalyst coated membrane material. As such, in accordance with the present methodology the Pt (and / or palladium and / or ruthenium) is removed first by oxidative leaching prior to applying the reductive leach to recover the iridium. After the platinum and iridium have been recovered from the waste catalyst coated membrane, it can be treated with a heated solvent to disperse the ionomer membrane and recover a dispersion of ionomer. The solvent used to disperse the ionomer can be selected from water, an aqueous basic solution, an organic solvent, an alcohol, or a mixture of an alcohol and water. The solvent used to disperse the ionomer can be heated at a temperature of: at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; no more than 400°C, 300°C, 275°C, or 250°C; or within a range defined by any combination of the aforementioned lower and upper limits. In one preferred methodology, the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent. Subsequently, after dispersal of the ionomer, the ionomer dispersion can then be subjected to an ion exchange process to re-protonate the ionomer in the dispersion. It has been found that this methodology is advantageous to achieve good dispersion of the ionomer material without damaging the ionomer material so long as the PGM material is removed prior to the ionomer dispersal process. As such, a preferred process flow as illustrated in Figure 3 is as follows: (i) oxidative acid leach to recover platinum (and / or palladium and / or ruthenium); (ii) reductive acid leach to recover iridium; (iii) treatment of remaining solid ionomer material with a base to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; (v) separating (e.g., via filtration) the ionomer dispersion from other components, e.g., carbon and / or membrane reinforcement material; and (vi) subjecting the ionomer dispersion to an ion exchange process to re-protonate the ionomer material. PGM recovery For water electrolyser materials, Ir has been recovered via a reductive leach, but these have shown varying levels of Pt recovery at the same time. In order to minimise this mixing of Pt and Ir chloride species, the Pt oxidative leach has been trialled first, followed by the reductive Ir leach. For reliability, this experiment has been repeated twice. Pt oxidative leach Five water electrolyser CCMs were shredded into pieces of 1 cm x 2 cm size. Total CCM mass was 21.23 g. A flange vessel equipped with an overhead stirrer, condenser with cooling water, temperature probe and stoppers in all vacant ports was set up on a hot plate. This was loaded with the CCMs and 395 mL 12M HCI added to it, with the solution yellowing immediately. This was set to stir at 200 rpm and the heat set to 70°C. When at temperature, 1.25 mL 30% peroxide was added to the vessel via a Watson Marlow peristaltic pump at 1 rpm for the first minute and then at 7 rpm for the remainder of the addition. This reaction was left heating for a further 50 minutes. Once complete, the heat was turned off and the reaction allowed to cool. This was filtered under vacuum with cellulose nitrate filter paper. Ir reductive leach The leached CCMs were suspended in 90 mL demineralized water in a beaker and 1.8 mL 35% hydrazine added dropwise whilst stirring. The CCMs greyed where in contact with hydrazine directly. This suspension was sonicated in an ultrasonic bath at room temperature for 5 minutes. The flange vessel was set up as before with the Pt leach. The CCM suspension was added to the flange vessel. 250 mL 12M HCI was added slowly, in increments, whilst stirring at 200 rpm. The CCM pieces began to break apart at this point. A sample was taken. The vessel was heated to 105°C. When at temperature, the timer was started and a sample taken every 1.5 hours for a total of 4.5 hours. After this, the reaction vessel was cooled and the suspension filtered via a vacuum. All samples were filtered under vacuum and then syringe filtered. Pt oxidative leach (repeated) The repeat experiment used the same method for the oxidative leach but removed the sonication step for the reductive leach. Mass of CCMs was 21.27 g, 400mL of 12M acid was used, heating was to 75 °C, and 1.5 mL of hydrogen peroxide was used. As before, heating was performed for 50 minutes. Ir reductive leach (repeated) The flange vessel was set up as before. The CCMs were added to the vessel with 90 mL demineralized water. This was set to stir at 130 rpm whilst 1.8 mL hydrazine was added dropwise. This was left to stir for 5 minutes. 250 mL of 12M HCI was added slowly whilst stirring at 300 rpm. As before, the vessel was heated to 105°C. When at temperature, the timer was started and a sample taken every 1.5 hours for a total of 4.5 hours. After this, the reaction vessel was cooled and the suspension filtered via a vacuum. All samples were filtered under vacuum and then syringe filtered. Results Discussion and Conclusions The CCMs showed successful Pt recovery (approximately 100% within experimental error) when carrying out the oxidative leach with selectivity for Pt. Following this, the reductive leach showed good recovery of Ir, with a stronger recovery in the repeat experiment (> 95%). Overall, >97% of the PGMs were recovered from the CCM material. Ionomer Recovery Anhydrous LiOH (6.0 g) was added to water (250 g) and the LiOH dissolved in the water. Membrane pieces were submerged in the LiOH solution and heated to reflux (1 hour). The resultant mixture was washed out with water (4 x 100 mL). The remaining water was decanted to leave (wet) membrane pieces. Water (250 g) was added to the (wet) membrane pieces and heated to reflux (1 hour). The water was then decanted and the solid product dried in vacuo. Figure 4 shows FTIR data showing salt formation. FTIR data was collected for untreated fluorinated polymer membrane material 301, fluorinated polymer salt material formed after treatment in the aqueous solution of LiOH 303, and fluorinated polymer salt material formed after treatment in the aqueous solution of LiOH followed by the water wash 304. Figure 5 shows an example of process steps (pre-autoclave). The membrane was brown in colouration as indicated in the figure. After being refluxed in the solution of lithium hydroxide the membrane turned colourless and converted to salt form as confirmed by spectroscopic analysis. The conversion was achieved without dispersing the membrane which remained in solid, undispersed form. In the final step of the pre-autoclave process shown in Figure 4, the solid polymer salt membrane material was washed in water to remove any residual LiOH solution. Figure 6 is a photograph showing the membrane before (left hand side) and after (right hand side) the process steps of refluxing the membrane in a basic LiOH solution and washing with water indicating the colour change of the membrane from brown to colourless and the fact that the membrane remained in solid, undispersed form. Spectroscopic analysis confirmed that the colourless membrane was in salt form. Figure 7 shows a further step of autoclaving the membrane following the treatment process as shown in Figure 5 to disperse the membrane in water. The colourless, solid, undispersed, polymer salt membrane was autoclaved in water under nitrogen at 250°C and 40 bar (4000 kPa) autogenous pressure. This resulted in a (non-basic) aqueous dispersion of the polymer salt. Figure 8 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form. An ion exchange column containing Amberlyst™ 15 (H) resin was utilized for this process step. The dispersion of (protonated) fluorinated polymer may be re-used to manufacture new membranes or dried and stored for future use. Summary The present specification provides a method of recycling ionomer waste materials to recover PGM and ionomer materials while providing good materials accounting and enabling the recycling process to produce ionomer products of a target specification to meet functional end use requirements. While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of recycling a waste ionomer material comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising:(a) mixing the waste ionomer material to homogenize the waste ionomer material;(b) taking a sample of the homogenized waste ionomer material;(c) assaying the sample of homogenized waste ionomer material to characterize ionomer content and platinum group metal content of the waste ionomer material; and(d) recycling the waste ionomer material to separate and recover both the ionomer and the platinum group metal materials on the basis of the ionomer content and the platinum group metal content determined by the assaying.

2. A method according to claim 1,wherein step (a) includes reducing particle size of the waste ionomer material.

3. A method according to claim 2,wherein the waste ionomer material is in the form of a membrane material which is shredded and mixed in step (a) to reduce particle size and homogenize.

4. A method according to any preceding claim,wherein step (b) includes processing the sample to further reduce particle size.

5. A method according to any preceding claim,wherein, in step (b), more than one sample of the homogenized waste ionomer material is taken for subsequent assaying in step (c).

6. A method according to any preceding claim,wherein the assaying in step (c) includes characterizing the sample for one or more other materials including one or more of base metal content, carbon content, and polymer reinforcement content in addition to the ionomer content and the platinum group metal content.

7. A method according to any preceding claim,wherein, in addition to determining the amount of platinum group metal and ionomer, the assaying in step (c) further includes determining one, more, or all of the following:platinum group metal type;ionomer equivalent weight(s);ionomer type(s);ionomer molecular weight(s);base metal type and amount;carbon content;polymer reinforcement material type and amount.

8. A method according to any preceding claim,wherein, after step (c), the assaying results for the ionomer are compared with a target composition for the ionomer after recycling in step (d), and in step (d) during recycling, additional ionomer material is blended with the waste ionomer material, the additional ionomer material being of a type and quantity to achieve the target composition for the ionomer.06 05 259. A method according to any preceding claim,wherein, after step (c), the waste ionomer material is mixed with one or more other waste ionomer materials prior to recycling in step (d).

10. A method according to any preceding claim,wherein the recycling in step (d) includes: treating the waste ionomer material with one or more acid leaches to extract the platinum group metal material; and an ionomer dispersal step to extract the ionomer material, the leaching and dispersal steps being performed in any order.

11. A method according to claim 10,wherein step (d) includes treating the waste ionomer material with a heated solution comprising an acid and an oxidant, wherein platinum, palladium, and / or ruthenium is leached from the waste catalyst coated membrane material into the solution which is separated from remaining solid components of the waste ionomer material.

12. A method according to claim 10 or 11,wherein step (d) includes leaching iridium from the waste ionomer material using a heated solution comprising an acid and a reducing agent and separating the solution comprising the leached iridium from remaining solid components of the waste ionomer material.

13. A method according to any one of claims 10 to 12,06 05 25wherein step (d) includes treating the waste ionomer material with a heated solvent to disperse the ionomer and recover a dispersion of ionomer.

14. A method according to claims 11 to 13,wherein the oxidative acid leach of claim 12 is performed prior to the reductive acid leach of claim 13 which is performed prior to the ionomer dispersion of claim 14.

15. A method according to claim 13 or 14,wherein the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent.

16. A method according to any one of claims 13 to 15,wherein the ionomer dispersion is filtered to remove carbon and / or polymer reinforcement material.

17. A method according to claim 16,wherein the filtered carbon and reinforcement material are dispersed in a solvent to form a slurry and separated by particle size.

18. A method according to any one of claims 13 to 17,wherein the ionomer dispersion is subjected to an ion exchange process to re-protonate the ionomer in the dispersion.

19. A method according to any preceding claims,wherein a membrane is fabricated using the recovered ionomer and said membrane is tested to confirm it meets a target specification.

Images